The present invention relates to a data storage, and in particular, to a distributed storage and a system using the same.
While an electronic commerce system and a data center are being constructed for practices, it is desired for a system to protect important data such as information of customers and commercial contents even in local disaster or catastrophe caused by, for example, an earthquake, a fire, and a power failure.
To protect data, a method called “redundant array of independent disks (RAID)” or “remote copy” has been heretofore employed. The RAID system is classified into RAID-0 to RAID-5. To protect data at a disk failure, RAID-0 and RAID-5 are mainly used at present.
In the RAID-1, the data to be protected is written on a current disk and another or backup disk. Even if the current disk fails, the data thereon is also written on the backup disk. It is therefore possible to prevent loss of data.
In the RAID-5 system, record data divided into blocks and parity of the record data are distributed to be recorded on a plurality of disks.
When one of the disks fails in the RAID-5 system, the record data on the disk can be restored using associated data and data parity stored on other normal disks. Also, since data can be distributively written on or read from the disks in a concurrent fashion in the RAID-5 system, the disk access speed is increased when compared with a disk access operation using one disk.
A remote copy method is used to produce a replica or copy of data at a physically remote location using a network. The remote copy is achieved, for example, in a configuration in which servers are coupled via a network with each other or a configuration in which storage subsystems are coupled via a network with each other. In this case, a leased communication line with guaranteed communication quality is primarily employed as the network for the remote copy.